Technical Field
This invention relates to the layout of memory cells and their associated pair of bit lines in such a way that very high density arrays are obtainable. The layout is accomplished without changing the process steps by which less dense arrays were obtained. The resulting memory cell array is one in which the bit lines associated with each column of memory cells are interleaved with the bit lines of adjacent columns of memory cells. By this means, regions of the semiconductor chip in which the cells are formed, which were formerly unusable, now become usable and cell area is significantly reduced. Because the spacing of metallic bit lines is governed by certain ground rules, cell length in the x-dimension could be reduced no further as long as metallic interconnections were used. To overcome this limitation without changing the process involved, polycrystalline fingers or extensions are substituted for metal cross-coupling interconnections. Because polycrystalline interconnections have less stringent requirements relative to their spacing, using such interconnections in conjunction with metallic straps which are shorter than the widths and spacing of two metallic interconnection lines again provides a significant reduction in the x-dimension and hence in cell area. When interleaved bit lines, polycrystalline fingers and straps are used at the same time instead of metal interconnections, both approaches provide a memory cell area which is significantly improved over cell areas when neither or only one of the approaches taught are used. The resulting cell is the densest cell obtainable using the same process steps. The method and structure taught may be utilized with both bipolar and unipolar devices.